Record NEXTHOP_PATH ATTIBUTE for BGP

In some BGP deployments, BGP next hops may use a set or tunnels or run across converged networks such as seamless MPLS. This document describes a new optional transitive path attribute, NEXTHOP_PATH ATTRIBUTE for BGP that records the next hop path which can be used by BGP network management to monitor and manage the BGP infrastructure via management interfaces (such as I2RS).